Grinding mill



Sept-8, 1931. I 1 s, s'n 1,822,435

GRINDING MILL Filed Feb. 15, 1950 CAD Patented Sept. 8, 1931- UNITEDSTATES.

PATENIT" OFFICE JOHAN S. FASTING, 0F VALBY, NEAR COPENHAGEN, DENMARK,ASSIGNOR TO F-L- SMIDTH & (30., OF NEW YORK, N. Y., A CORPORATION OF NEWJERSEY GRINDING MILL Application filed February 15, 1930, Serial No.428,640, and in Great Britain September 24, 1929.

This invention relates to grinding mills of the type generally calledtube mills, designed for the grinding of cement and the like, in whichthe material to be ground is placed, with grinding bodies, in acompartment of a rotating cylinder and is reduced to a more or lessfinely divided condition by impact of the grinding bodies in therotation of the mill. Such mills are commonly provided with transversepartitions which form successive compartments, from one to another ofwhich the material being ground passes as its particles reduce in size."In such mills the grinding bodies themselves are commonly proportionedproperly with respect to the fineness of the material in successivecompartments, it having been found that the efficiency of such a mill ismaterially reduced if'the grinding bodies in the successive compartmentsare not suited to the progressive fineness of the material in successivecompartments. In the operation of such mills the material undergoes apreliminary grinding in the first chamber or compartment, in which thegrinding bodies are of such size that they will with certainty crush thelargest pieces of material supplied to the preliminary chamber. Fromthis first chamber the par ticles of material which have been reduced insize pass through openings in the transverse wall or partition into thenext chamber where smaller grinding bodies continue the grindingoperation and so on throughout the successive chambers of the mill. Inthis manner the grinding bodies may be in some degree suited 'to, thefineness of some of the material in the chamber, but it will be readilyunderstood that in the processof grinding some of the particles ofmaterial are reduced in size much more than are other particles and aretoo small for the proper action of the grinding bodies with which thecompartment is charged. Infact, the material as it is supplied to thefirst or preliminary chamber may contain grains or particles which arealready smaller than those for which the grinding bodies in that chamberhave been selected. A similar condition exists in the successivechambers, in

each of .which there is more or less material which is too. finelydivided'for proper action of the grinding bodies and the presence ofwhich clogs the action of the grinding bodies on the larger particlesand so reduces the efliciency of the mill.

This difliculty in the operation of tube mills has been well recognizedand efforts have been made to overcome the difficulty, as by increasingthe screening action of the transverse partition or wall which forms theend of the chamber, as by fitting the partition on its rearward facewith projections extending rearwardly into the chamber so as to come incontact with the material contained in the feeding end of thecompartment. It has also been proposed to provide the partition or endwall with openings so large that large quantities of the material may"pass through and then be subjected to the action of screening deviceswhereby the finer :material may be passed on to the next cham ber whilethe coarser material is returned to the chamber for further grindingaction.

Such efforts have been only partially sucoessful, being effective onlyon the material in the chamber near the end wall through whichit is topass into the next chamber and failing to effect operation on the finermaterial near the feeding end of the chamber, whereit continues to clogthe action of the grinding bodies and reduce the efficiency of the mill.

It has been the object of the present invention to overcome stillfurther the difiiculty referred to and to'that end the construction ofthe mill has been so modified as to provide for the separation of thefiner material from the coarser throughout the length of thecompartment,so that the action of the grlnding bodies on the coarserlsno longer clogged, but the grinding bodies are relieved from action onthe liner particles and their percussive effect is exerted more fully onthe coarser material, with resultingincreased efliciency of thematerial. Since the separation of the finer material is more completelyeffected when it carries with it some particles or grains which aretoolarge for introduction into the next grindingchamher, there is alsoprovided, external to the grinding chamber, a screening device whichserves to separate the material that is too coarse to be admitted to thenext grinding chamber but should be returned for further grinding in thechamber from which it passed with the finer material. The constructionof the screening device is such that inspection of the interior surfaceof the compartment and replacement of Worn parts are readily possible.

The invention will be more fully explained hereinafter with reference tothe accompanying drawings in which:

Figure I is a View in longitudinal section of so much of a tube mill asis necessary to enable the application of the invention to beunderstood.

Figure II is a View in transverse section on the plane indicated by thebroken line II-II of Figure I.

In the drawings there is shown only the preliminary grinding chamber ofa tube mill, with its appurtenances, but it will be understood that thesame or similar appurtenances might be applied to the mill in connectionwith each or any of the succeeding chambers or compartments. In. theconstruction shown the grinding chamber is provided with a series ofnon-concentric grinding plates 1 which are so arranged that the trailingedge of each plate overlaps inwardly the leading edge of the next plate,the plates being secured to each other and to the shell 1 of the mill bybolts 2. which pass through the plates and through the shell, as shownin Figure I, and receive nuts 2 on their outer ends so that they may beremoved readily for inspection and replacement. An opening 3 for thepassage inwardly of the material being ground is provided between thetrailing edge of each plate and the leading edge of the next plate. Theplates 1 extend from end to end of the chamber and may contact at theirends on transverse plates 4 and 5, the former being provided centrallywith an aperture 6 through which the material to be ground may beintroduced into the chamber from a chute 7. Each plate 1 is alsoprovided, preferably near its leading edge, with apertures 8 throughwhich the finer material may pass outwardly in the operation of themill. It will be understood that the shell l of the mill is sectional,or formed with openings 1 between the leading edge of each section andthe trailing edge of the preceding section, through which openings thematerial being ground may pass from the openings 3.

External to the shell 1 and overlapping the openings 1" are screens 9,preferably curved, as shown and secured at their edges to the sectionsof the shell 1 and within each screen 9 is placed a bafile or guideplate 11, preferabl curved as shown, its function being to receive thematerial from the holes 8 of the grinding plates and, in the rotation ofthe mill, to discharge the material upon the screen 9 near its leadingedge, so that in the continued rotation of the mill the material willpass over practically the can tire screen surface, the finer particlespassing through the screen and the coarser being returned. to theinterior of the grinding chamber through the openings 3.

The finer particles which have passed through the screens 9 are receivedwithin a frusto-conical jacket 12 and in the rotation of the mill, passtoward the end of greater diameter, where the material is lifted byscoops 13 and, as each scoop reaches its highest point, is dischargedupon a central cone 15, carried by the end plate 5" and is therebydirected through a central opening 16, in a transverse plate 14, intothe next grinding chamber 17.

In a mill constructed as described the material introduced into thegrinding chamber through the inlet opening, such as the opening 6, issubjected to the action of the grinding bodies 18. Such of the materialas is already sufficiently fine to pass through the openings 8 or isreduced by the grinding bodies to such fineness escapes from theinterior of the grinding chamber through the openings 8 throughout thelength of the chamber and is screened by the screens 9. Such of thematerial. as is too coarse to pass through the screens 9 is returnedinto the grinding chamber while the material which is sufiiciently fineto pass through the screen is raised by the shovels 13 and is dischargedby the shovels and cone 15 into the next grinding chamber 17. y

The assembling, inspection and replacement of parts of the grindingchamber may be effected readily as the nuts 2 of the bolts 2 areaccessible from the outside and each screen 9 is independent of theother screens and may be replaced independently of the others.

It will be understood that various changes in details of constructionand arrangement can be made to suit different conditions of use and thatthe invention, except as pointed out in the accompanying claim, is notlimited to the particular construction shown and described herein.

I claim as my invention:

The combination in a tube mill of a shell formed with openingstherethrough, grindmg plates forming a grinding chamber and securedwithin the shell and overlapping the openings within the shell, openingsbeing provided for the passage of ground material from the interior ofthe grinding chamber outwardly through the grinding plates and for thereturn of the material inwardly into the grinding chamber, screenssecured to the shell and overlapping the openings therethrough, saidscreens permitting the finer material to pass through the same andserving to return the coarser material to the grinding chamber, andguide plates, one Within each screen, to direct the material receivedthrough the openings of the grinding plates upon the leading portion ofthe screen.

This application signed this 25th day of January, A. D. 1930.

J OHAN S. FASTING.

